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102-421: A nap is a short period of sleep , typically taken during daytime hours as an adjunct to the usual nocturnal sleep period. Naps are most often taken as a response to drowsiness during waking hours. A nap is a form of biphasic or polyphasic sleep , where the latter terms also include longer periods of sleep in addition to one period. For years, scientists have been investigating the benefits of napping, including
204-405: A 24-hour cycle, whereas in monophasic sleep this occurs all at once. Under experimental conditions, humans tend to alternate more frequently between sleep and wakefulness (i.e., exhibit more polyphasic sleep) if they have nothing better to do. Given a 14-hour period of darkness in experimental conditions, humans tended towards bimodal sleep, with two sleep periods concentrated at the beginning and at
306-407: A brain area directly above the optic chiasm , is presently considered the most important nexus for this process; however, secondary clock systems have been found throughout the body. An organism whose circadian clock exhibits a regular rhythm corresponding to outside signals is said to be entrained ; an entrained rhythm persists even if the outside signals suddenly disappear. If an entrained human
408-524: A child's quality of sleep as well as prepare them to make and keep healthy sleep hygiene habits in the future. Children need many hours of sleep per day in order to develop and function properly: up to 18 hours for newborn babies, with a declining rate as a child ages. Early in 2015, after a two-year study, the National Sleep Foundation in the US announced newly revised recommendations as shown in
510-905: A decreased inclination for daytime sleep compared to younger counterparts, and this decline persists even when accounting for variations in habitual sleep duration. This age-related decrease in daytime sleep propensity is evident in middle-aged individuals and coincides with statistically significant reductions in total sleep time, slow-wave sleep (SWS), and slow-wave activity (SWA). Sex differences have also been found, such that females tend to have higher levels of SWS compared to males, at least up until menopause. Older individuals exhibit gender-based variations in non-rapid eye movement (NREM) sleep, where women demonstrate increased slow-wave sleep (SWS) during both regular and recuperative sleep, along with higher occurrences of stage 3 and 4 which are considered as NREM sleep. There have also been studies that have shown differences between races. The results showed that there
612-414: A factor which may exacerbate disruption of the circadian cycle. Scientific studies on sleep have shown that sleep stage at awakening is an important factor in amplifying sleep inertia . Determinants of alertness after waking up include quantity/quality of the sleep, physical activity the day prior, a carbohydrate-rich breakfast, and a low blood glucose response to it. Sleep timing is controlled by
714-440: A family suggests that heredity may be a potential cause of this disorder. J. A. Horne (1978) reviewed several experiments with humans and concluded that sleep deprivation has no effects on people's physiological stress response or ability to perform physical exercise. It did, however, have an effect on cognitive functions. Some people reported distorted perceptions or hallucinations and lack of concentration on mental tasks. Thus,
816-616: A full eight hours. Researchers have found that sleeping 6–7 hours each night correlates with longevity and cardiac health in humans, though many underlying factors may be involved in the causality behind this relationship. Sleep difficulties are furthermore associated with psychiatric disorders such as depression , alcoholism , and bipolar disorder . Up to 90 percent of adults with depression are found to have sleep difficulties. Dysregulation detected by EEG includes disturbances in sleep continuity, decreased delta sleep and altered REM patterns with regard to latency, distribution across
918-413: A function of slow wave sleep is to facilitate the healing of muscles as well as repair damage to tissues. Lastly, glial cells within the brain are restored with sugars to provide energy for the brain. Learning and memory formation occurs during wakefulness by the process of long-term potentiation ; SWS is associated with the regulation of synapses thus potentiated. SWS has been found to be involved in
1020-407: A function of the amount of time elapsed since the last adequate sleep episode) must be balanced against the circadian element for satisfactory sleep. Along with corresponding messages from the circadian clock, this tells the body it needs to sleep. The timing is correct when the following two circadian markers occur after the middle of the sleep episode and before awakening: maximum concentration of
1122-413: A good night's sleep. The American Academy of Sleep Medicine (AASM) divides NREM into three stages: N1, N2, and N3, the last of which is also called delta sleep or slow-wave sleep . The whole period normally proceeds in the order: N1 → N2 → N3 → N2 → REM. REM sleep occurs as a person returns to stage 2 or 1 from a deep sleep. There is a greater amount of deep sleep (stage N3) earlier in the night, while
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#17328631084041224-418: A longer nap. Sleep inertia is less intense after short naps. Sleep latency is shorter when a nap is taken between 3 and 5 pm, compared with a nap taken between 7 and 9 pm. According to The Sleep Foundation, Psychology Today and Harvard Health Publishing, these are the best practices for napping: Sleep Sleep is a state of reduced mental and physical activity in which consciousness
1326-436: A lower amplitude of slow-wave activity (SWA) compared to healthy participants. Sex differences also persist in the former group: depressed men present significantly lower SWA amplitude. This sex divergence is twice as large as the one observed in healthy subjects. However, no age-related difference concerning SWS can be observed in the depressed group. During sleep, the distribution of slow-wave activity (SWA) typically exhibits
1428-418: A particular frequency corresponds to various points in the sleep-wake cycle, such as being asleep, being awake, or falling asleep. Alpha, beta, theta, gamma, and delta waves are all seen in the different stages of sleep. Each waveform maintains a different frequency and amplitude. Alpha waves are seen when a person is in a resting state, but is still fully conscious. Their eyes may be closed and all of their body
1530-419: A period of sleep. Furthermore, slow-wave sleep improves declarative memory (which includes semantic and episodic memory). A central model has been hypothesized that the long-term memory storage is facilitated by an interaction between the hippocampal and neocortical networks. In several studies, after the subjects have had training to learn a declarative memory task, the density of human sleep spindles present
1632-408: A person naps affects sleep inertia and sleep latency : a person is more likely to benefit in terms of those two points when they sleep moderately in the afternoon. According to research, the degree to which a person experiences sleep inertia differs in different durations of nap. Because sleep inertia is possibly resulting from awakening from slow-wave sleep , it is more likely to happen when one has
1734-458: A positive feedback loop. This recurrent excitation is balanced by inhibition, resulting in the active state of the slow oscillation of slow wave sleep. Failure of this mechanism results in a silencing of activity for a brief period of time. The recurrence of active and silent periods occurs at a rate of 0.5–4 Hz, giving rise to the slow waves of the EEG seen during slow wave sleep. Slow-wave sleep
1836-459: A prevalence in the frontal region of the brain. In the subsequent recovery sleep after experiencing sleep deprivation , the frontal cortex exhibits the most significant rise in slow-wave activity (SWA) compared to the temporal region , parietal region , and occipital region . The notable increase in SWA following sleep deprivation in the frontal areas, coupled with the prevailing presence of SWA in
1938-431: A role during this period of sleep. Also, these neurons appear to have some sort of internal dialogue, which accounts for the mental activity during this state where there is no information from external signals (because of the synaptic inhibition at the thalamic level). The rate of recall of dreams during this state of sleep is relatively high compared to the other levels of the sleep cycle. This indicates that mental activity
2040-503: A role in the rising demand for daytime naps: sleepiness rises towards the mid-afternoon, hence the best timing for naps is early afternoon. Twenty- to thirty-minute naps are recommended for adults, while young children and elderly people may need longer naps. Research, on the other hand, has shown that the benefits of napping depend on sleep onset and sleep phases rather than time and duration. The state of grogginess, impaired cognition and disorientation experienced when awakening from sleep
2142-445: A screen before bed may interfere with sleep. Modern humans often find themselves desynchronized from their internal circadian clock, due to the requirements of work (especially night shifts ), long-distance travel, and the influence of universal indoor lighting. Even if they have sleep debt, or feel sleepy, people can have difficulty staying asleep at the peak of their circadian cycle. Conversely, they can have difficulty waking up in
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#17328631084042244-430: A strong relationship between amyloid-b and SWA, pointing out that increased disruption in SWA is correlated with elevated levels of amyloid-b. Hence, Slow waves of non-rapid eye movement sleep, or NREM sleep, are disrupted or decrease when amyloid beta (Aβ) builds up in the prefrontal cortex. As a result, this may hinder older people' capacity for memory consolidation . Moreover, the onset of Alzheimer's disease (AD)
2346-438: A structured bedtime routine. This can look differently among families, but will generally consist of a set of rituals such as reading a bedtime story, a bath, brushing teeth, and can also include a show of affection from the parent to the child such a hug or kiss before bed. A bedtime routine will also include a consistent time that the child is expected to be in bed ready for sleep. Having a reliable bedtime routine can help improve
2448-611: A subjective point of view. Objective sleep quality refers to how difficult it is for a person to fall asleep and remain in a sleeping state, and how many times they wake up during a single night. Poor sleep quality disrupts the cycle of transition between the different stages of sleep. Subjective sleep quality in turn refers to a sense of being rested and regenerated after awaking from sleep. A study by A. Harvey et al. (2002) found that insomniacs were more demanding in their evaluations of sleep quality than individuals who had no sleep problems. Homeostatic sleep propensity (the need for sleep as
2550-540: A transitional period is called slow-wave sleep or deep sleep. During this phase, body temperature and heart rate fall, and the brain uses less energy. REM sleep, also known as paradoxical sleep, represents a smaller portion of total sleep time. It is the main occasion for dreams (or nightmares ), and is associated with desynchronized and fast brain waves, eye movements, loss of muscle tone, and suspension of homeostasis . The sleep cycle of alternate NREM and REM sleep takes an average of 90 minutes, occurring 4–6 times in
2652-491: A vibrating stimulus was put on the hand of human subjects. The recordings show an important inter-hemispheric change during the first hour of non-REM sleep and consequently the presence of a local and use-dependent aspect of sleep. Another experiment detected a greater number of delta waves in the frontal and central regions of the right hemisphere. Considering that SWS is the only sleep stage that reports human deep sleep as well as being used in studies with mammals and birds, it
2754-522: Is adenosine , a neurotransmitter that inhibits many of the bodily processes associated with wakefulness. Adenosine levels increase in the cortex and basal forebrain during prolonged wakefulness, and decrease during the sleep-recovery period, potentially acting as a homeostatic regulator of sleep. Coffee , tea, and other sources of caffeine temporarily block the effect of adenosine, prolong sleep latency, and reduce total sleep time and quality. Humans are also influenced by aspects of social time , such as
2856-525: Is a drug commonly used to treat Parkinson's disease which acts to increases the brain's dopamine availability. Nocturnal single doses of levodopa have been shown to increase SWS by 10.6% in elderly. Antagonists of certain serotonergic receptors (namely 5-HT 2A and 5-HT 2C ) have also been demonstrated to enhance SWS sleep, although they do not consistently bring about improvements in overall sleep duration or symptoms associated with insomnia . Trazodone , an atypical antidepressant , increases
2958-541: Is a highly conserved behavior across animal evolution, likely going back hundreds of millions of years. Humans may suffer from various sleep disorders , including dyssomnias , such as insomnia , hypersomnia , narcolepsy , and sleep apnea ; parasomnias , such as sleepwalking and rapid eye movement sleep behavior disorder ; bruxism ; and circadian rhythm sleep disorders . The use of artificial light has substantially altered humanity's sleep patterns. Common sources of artificial light include outdoor lighting and
3060-481: Is a prominent brain rhythm during NREM sleep. Similarly, even cognitively healthy individuals with detectable amyloid beta exhibit sleep disturbances , characterized by compromised sleep quality and an increased frequency of daytime napping. Though SWS is fairly consistent within the individual, it can vary across individuals. To some degree, individual variations seem to be influenced by demographic factors such as gender and age. Age and sex have been noted as two of
3162-552: Is accumulated against an individual's average sleep or some other benchmark. It is also unclear whether the prevalence of sleep debt among adults has changed appreciably in the industrialized world in recent decades. Sleep debt does show some evidence of being cumulative. Subjectively, however, humans seem to reach maximum sleepiness 30 hours after waking. It is likely that in Western societies , children are sleeping less than they previously have. One neurochemical indicator of sleep debt
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3264-433: Is also adopted in experiments revealing the role of hemispheric asymmetries during sleep. A predominance of the left hemisphere in the neural activity can be observed in the default-mode network during SWS. This asymmetry is correlated with the sleep onset latency , which is a sensitive parameter of the so-called first night effect—the reduced quality of sleep during the first session in the laboratory. The left hemisphere
3366-419: Is altered and certain sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with the surrounding environment. While sleep differs from wakefulness in terms of the ability to react to stimuli , it still involves active brain patterns, making it more reactive than a coma or disorders of consciousness . Sleep occurs in repeating periods , during which
3468-441: Is always greatest during this stage. It is also thought to be responsible for a decrease in sympathetic and increase in parasympathetic neural activity. Large 75-microvolt (0.5–2.0 Hz) delta waves predominate the electroencephalogram (EEG). Stage N3 is defined by the presence of 20% delta waves in any given 30-second epoch of the EEG during sleep, by the current 2007 AASM guidelines. Longer periods of SWS occur in
3570-402: Is characterized by a higher prevalence of spindles, while slow waves dominate the EEG during stage 3. Slow-wave sleep is an active phenomenon probably brought about by the activation of serotonergic neurons of the raphe system. The slow-wave seen in the cortical EEG is generated through recurrent connections within the cerebral cortex, where cortical pyramidal cells excite one another in
3672-400: Is closer to real life events. Slow-wave sleep is the constructive phase of sleep for recuperation of the mind-body system in which it rebuilds itself after each day. Substances that have been ingested into the body while an organism is awake are synthesized into complex proteins of living tissue. Growth hormone is also secreted during this stage, which leads some scientists to hypothesize that
3774-564: Is correlated to the regional asymmetry in the activities of SWS. These findings show that the hemispheric asymmetry in SWS plays a role as a protective mechanism. SWS is therefore sensitive to danger and non-familiar environment, creating a need for vigilance and reactivity during sleep. Several neurotransmitters are involved in sleep and waking patterns: acetylcholine, norepinephrine, serotonin , histamine, and orexin . Neocortical neurons fire spontaneously during slow-wave sleep, thus they seem to play
3876-399: Is isolated in a bunker with constant light or darkness, he or she will continue to experience rhythmic increases and decreases of body temperature and melatonin, on a period that slightly exceeds 24 hours. Scientists refer to such conditions as free-running of the circadian rhythm. Under natural conditions, light signals regularly adjust this period downward, so that it corresponds better with
3978-450: Is known as a "natural short sleeper". This condition is not to be confused with intentional sleep deprivation, which leaves symptoms such as irritability or temporarily impaired cognitive abilities in people who are predisposed to sleep a normal amount of time but not in people with FNSS. The genes DEC2 , ADRB1 , NPSR1 and GRM1 are implicated in enabling short sleep. The quality of sleep may be evaluated from an objective and
4080-457: Is known as sleep inertia. This state reduces the speed of cognitive tasks but has no effects on the accuracy of task performance. The effects of sleep inertia rarely last longer than 30 minutes in the absence of prior sleep deprivation. A 2016 meta-analysis showed that there may be a correlation between habitual napping for more than an hour, and having an increased risk for cardiovascular disease , diabetes , metabolic syndrome or death. There
4182-503: Is marked by the deposition of amyloid beta (Aβ) in the brain. AD is distinguished by the presence of amyloid-beta plaques and neurofibrillary tangles . These structural anomalies are linked to disruptions in the sleep-wake cycle, particularly in non-rapid eye movement (NREM), slow wave sleep (SWS). Thus, individuals diagnosed with Alzheimer's often experience disturbances in sleep, resulting in diminished levels of non-rapid eye movement (NREM) sleep and reduced slow wave activity (SWA), that
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4284-407: Is more important than the other stages. During slow-wave sleep, there is a significant decline in cerebral metabolic rate and cerebral blood flow . The activity falls to about 75 percent of the normal wakefulness level. The regions of the brain that are most active when awake have the highest level of delta waves during slow-wave sleep. This indicates that rest is geographical. The "shutting down" of
4386-423: Is necessary during SWS in order to consolidate sleep-related declarative memory. Sleep deprivation studies with humans suggest that the primary function of slow-wave sleep may be to allow the brain to recover from its daily activities. Glucose metabolism in the brain increases as a result of tasks that demand mental activity. Another function affected by slow-wave sleep is the secretion of growth hormone , which
4488-418: Is necessary for survival. Some animals, such as dolphins and birds, have the ability to sleep with only one hemisphere of the brain, leaving the other hemisphere awake to carry out normal functions and to remain alert. This kind of sleep is called unihemispheric slow-wave sleep , and is also partially observable in human beings. Indeed, a study reported a unilateral activation of the somatosensorial cortex when
4590-422: Is observed to be a necessary behavior across most of the animal kingdom, including some of the least cognitively advanced animals which have no need for other functions of sleep, such as memory consolidation or dreaming. It has been widely accepted that sleep must support the formation of long-term memory, and generally increasing previous learning and experiences recalls. However, its benefit seems to depend on
4692-443: Is profoundly influenced by changes in light, since these are its main clues about what time it is. Exposure to even small amounts of light during the night can suppress melatonin secretion, and increase body temperature and wakefulness. Short pulses of light, at the right moment in the circadian cycle, can significantly 'reset' the internal clock. Blue light, in particular, exerts the strongest effect, leading to concerns that use of
4794-400: Is regulated by a process called homeostasis . Induced or perceived lack of sleep is called sleep deprivation . Process S is driven by the depletion of glycogen and accumulation of adenosine in the forebrain that disinhibits the ventrolateral preoptic nucleus , allowing for inhibition of the ascending reticular activating system . Sleep deprivation tends to cause slower brain waves in
4896-443: Is resting and relatively still, where the body is starting to slow down. Beta waves take over alpha waves when a person is at attention, as they might be completing a task or concentrating on something. Beta waves consist of the highest of frequencies and the lowest of amplitude, and occur when a person is fully alert. Gamma waves are seen when a person is highly focused on a task or using all their concentration. Theta waves occur during
4998-429: Is shown to be more sensitive to deviant stimuli during the first night—compared to the following nights of an experiment. This asymmetry explains further the reduced sleep of half the brain during SWS. Indeed, in comparison to the right one, the left hemisphere plays a vigilant role during SWS. Furthermore, a faster behavioral reactivity is detected in the left hemisphere during SWS of the first night. The rapid awakening
5100-433: Is sleep-related eating disorder. An individual will sleep-walk leaving his or her bed in the middle of the night seeking out food, and will eat not having any memory of the event in the morning. Over half of individuals with this disorder become overweight. Sleep-related eating disorder can usually be treated with dopaminergic agonists , or topiramate , which is an anti-seizure medication . This nocturnal eating throughout
5202-450: Is the third stage of non-rapid eye movement sleep (NREM), where electroencephalography activity is characterised by slow delta waves . Slow-wave sleep usually lasts between 70 and 90 minutes, taking place during the first hours of the night. SWS is characterised by moderate muscle tone, slow or absent eye movement, and lack of genital activity. Slow-wave sleep is considered important for memory consolidation , declarative memory , and
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#17328631084045304-643: The American Academy of Sleep Medicine (AASM) divided slow-wave sleep into stages 3 and 4. The two stages are now combined as Stage three or N3. An epoch (30 seconds of sleep) which consists of 20% or more slow-wave (delta) sleep is now considered to be in slow-wave sleep. Slow-wave sleep is considered important for memory consolidation . This is sometimes referred to as "sleep-dependent memory processing". Impaired memory consolidation has been seen in individuals with primary insomnia, who thus do not perform as well as those who are healthy in memory tasks following
5406-488: The circadian clock (Process C), sleep-wake homeostasis (Process S), and to some extent by the individual will. Sleep timing depends greatly on hormonal signals from the circadian clock, or Process C, a complex neurochemical system which uses signals from an organism's environment to recreate an internal day–night rhythm. Process C counteracts the homeostatic drive for sleep during the day (in diurnal animals) and augments it at night. The suprachiasmatic nucleus (SCN),
5508-437: The frontal cortex , shortened attention span, higher anxiety, impaired memory, and a grouchy mood. Conversely, a well-rested organism tends to have improved memory and mood. Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. There is disagreement on how much sleep debt is possible to accumulate, and whether sleep debt
5610-592: The hippocampus during SWS is detected after the spatial learning task. In addition, a correlation can be observed between the amplitude of hippocampal activity during SWS and the improvement in spatial memory performance, such as route retrieval, on the following day. Additionally, studies have found that when odour cues are given to subjects during sleep, this stage of sleep excluslvely allows contextual cues to be reactivated after sleep, favoring their consolidation. A separate study found that when subjects hear sounds associated with previously shown pictures of locations,
5712-409: The immune , nervous , skeletal , and muscular systems; these are vital processes that maintain mood , memory , and cognitive function , and play a large role in the function of the endocrine and immune systems . The internal circadian clock promotes sleep daily at night , when it is dark. The diverse purposes and mechanisms of sleep are the subject of substantial ongoing research. Sleep
5814-440: The 30-minute nap as well as sleep durations of 1–2 hours. Performance across a wide range of cognitive processes has been tested. Sara Mednick conducted a study experimenting on the effects of napping, caffeine, and a placebo. Her results showed that a 60–90-minute nap is more effective than caffeine in memory and cognition. A power nap , also known as a Stage 2 nap, is a short slumber of 20 minutes or less which terminates before
5916-690: The United States, GHB is a prescription drug under the brand name Xyrem . It has been shown to reduce cataplexy attacks and excessive daytime sleepiness in patients with narcolepsy . The administration of the GABA a agonist gabaxadol enhances both deep sleep while also positively impacting various indicators of insomnia. Tiagabine , a selective gamma-aminobutyric acid (GABA) reuptake inhibitor, demonstrated to shown to improve sleep maintenance and to significantly increase SWS in healthy elderly subjects and adult patients with primary insomnia . Levodopa
6018-519: The amplitude of 12–14 Hz oscillations, K complexes lasting at least 0.5 seconds, consisting of a distinct negative sharp wave followed by a positive component, and slow waves or delta waves characterized by slow frequency (< 2 Hz) and high amplitude (> 75 μV) are key indicators. The presence and distribution of sleep spindle activity and slow waves vary across NREM sleep, leading to its subdivision into stages 1–3. While slow waves and sleep spindles are present in stages 2 and 3, stage 2 sleep
6120-433: The biggest factors that affect this period of sleep. Slow-wave sleep (SWS) and slow-wave activity (SWA) undergo significant transformations throughout one's lifespan, with aging serving as a particularly influential factor in predicting individual variations. Aging is inversely proportional to the amount of SWS beginning by midlife, so SWS declines with age. Moreover, recent findings indicate that older individuals exhibit
6222-447: The body alternates between two distinct modes: REM and non-REM sleep . Although REM stands for "rapid eye movement", this mode of sleep has many other aspects, including virtual paralysis of the body. Dreams are a succession of images, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep. During sleep, most of the body's systems are in an anabolic state, helping to restore
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#17328631084046324-486: The brain accounts for the grogginess and confusion if someone is awakened during deep sleep, since it takes the cerebral cortex time to resume its normal functions. According to J. Siegel (2005), sleep deprivation results in the build-up of free radicals and superoxides in the brain. Free radicals are oxidizing agents that have one unpaired electron, making them highly reactive. These free radicals interact with electrons of biomolecules and damage cells. In slow-wave sleep,
6426-415: The brain and body, the reduced rate of metabolism enables countervailing restorative processes. The brain requires sleep for restoration, whereas these processes can take place during quiescent waking in the rest of the body. The essential function of sleep may be its restorative effect on the brain: "Sleep is of the brain, by the brain and for the brain." This theory is strengthened by the fact that sleep
6528-551: The brain regions implicated in the induction of slow-wave sleep include: Some drugs influence sleep architecture by encroaching upon or prolonging deep sleep. Many drugs known to increase deep sleep in humans are of the GABAergic, dopaminergic, and anti-serotonergic classes. Gamma-hydroxybutyrate (GHB) is synthesized in the central nervous system (CNS) from gamma-aminobutyric acid (GABA). Oral administration of GHB has been shown to enhance SWS without suppressing REM sleep. In
6630-560: The brain restores its supply of adenosine triphosphate (ATP), the molecule used for short-term storage and transport of energy. In quiet waking, the brain is responsible for 20% of the body's energy use, thus this reduction has a noticeable effect on overall energy consumption. Sleep increases the sensory threshold . In other words, sleeping persons perceive fewer stimuli, but can generally still respond to loud noises and other salient sensory events. During slow-wave sleep , humans secrete bursts of growth hormone . All sleep, even during
6732-654: The day, is associated with the secretion of prolactin . Key physiological methods for monitoring and measuring changes during sleep include electroencephalography (EEG) of brain waves , electrooculography (EOG) of eye movements, and electromyography (EMG) of skeletal muscle activity. Simultaneous collection of these measurements is called polysomnography , and can be performed in a specialized sleep laboratory . Sleep researchers also use simplified electrocardiography (EKG) for cardiac activity and actigraphy for motor movements. The electrical activity seen on an EEG represents brain waves. The amplitude of EEG waves at
6834-407: The decreased rate of metabolism reduces the creation of oxygen byproducts, thereby allowing the existing radical species to clear. This is a means of preventing damage to the brain. Results from a number of research have shown how sleep affects Aβ dynamics. A good candidate for slow wave activity (SWA), which occurs during deep non-REM sleep, is amyloid-b modulation. The researchers also highlighted
6936-926: The deepest period of sleep. Napping too long and entering the slow wave cycles can make it difficult to awake from the nap and leave one feeling unrested. This period of drowsiness is called sleep inertia . The siesta habit has recently been associated with a 37% lower coronary mortality, possibly due to reduced cardiovascular stress mediated by daytime sleep. Short naps at mid-day and mild evening exercise were found to be effective for improved sleep, cognitive tasks, and mental health in elderly people. Monozygotic (identical) but not dizygotic (fraternal) twins tend to have similar sleep habits. Neurotransmitters, molecules whose production can be traced to specific genes, are one genetic influence on sleep that can be analyzed. The circadian clock has its own set of genes. Genes which may influence sleep include ABCC9 , DEC2 , Dopamine receptor D2 and variants near PAX 8 and VRK2 . While
7038-625: The downscaling of synapses, in which strongly stimulated or potentiated synapses are kept while weakly potentiated synapses either diminish or are removed. This may be helpful for recalibrating synapses for the next potentiation during wakefulness and for maintaining synaptic plasticity . Notably, new evidence is showing that reactivation and rescaling may be co-occurring during sleep. Bedwetting , night terrors , and sleepwalking are all common behaviors that can occur during stage three of sleep. These occur most frequently amongst children, who then generally outgrow them. Another problem that may arise
7140-505: The end of the dark time. Bimodal sleep in humans was more common before the Industrial Revolution . Different characteristic sleep patterns, such as the familiarly so-called " early bird " and " night owl ", are called chronotypes . Genetics and sex have some influence on chronotype, but so do habits. Chronotype is also liable to change over the course of a person's lifetime. Seven-year-olds are better disposed to wake up early in
7242-558: The end of the sleep cycle. Awakening involves heightened electrical activation in the brain, beginning with the thalamus and spreading throughout the cortex . On a typical night of sleep, there is not much time that is spent in the waking state. In various sleep studies that have been conducted using the electroencephalography, it has been found that females are awake for 0-1% during their nightly sleep while males are awake for 0-2% during that time. In adults, wakefulness increases, especially in later cycles. One study found 3% awake time in
7344-486: The exact 24 hours of an Earth day. The circadian clock exerts constant influence on the body, affecting sinusoidal oscillation of body temperature between roughly 36.2 °C and 37.2 °C. The suprachiasmatic nucleus itself shows conspicuous oscillation activity, which intensifies during subjective day (i.e., the part of the rhythm corresponding with daytime, whether accurately or not) and drops to almost nothing during subjective night. The circadian pacemaker in
7446-533: The first ninety-minute sleep cycle, 8% in the second, 10% in the third, 12% in the fourth, and 13–14% in the fifth. Most of this awake time occurred shortly after REM sleep. Today, many humans wake up with an alarm clock ; however, people can also reliably wake themselves up at a specific time with no need for an alarm. Many sleep quite differently on workdays versus days off, a pattern which can lead to chronic circadian desynchronization. Many people regularly look at television and other screens before going to bed,
7548-407: The first part of the night, primarily in the first two sleep cycles (roughly three hours). Children and young adults will have more total SWS in a night than older adults. The elderly may not go into SWS at all during many nights of sleep. NREM sleep, as observed on the electroencephalogram (EEG), is distinguished by certain characteristic features. Sleep spindles , marked by spindle-like changes in
7650-429: The frontal regions even during baseline sleep, has been construed as evidence supporting the involvement of slow-wave sleep (SWS) in functions typically linked to the frontal cortices. Thus, the prevalence of slow-wave sleep (SWS) in the frontal regions, particularly those linked to advanced cognitive functions or cognitive regions highly active during wakefulness, underscores the considerable importance of SWS. Some of
7752-412: The highest rate of sleep. The hours that children spend asleep influence their ability to perform on cognitive tasks. Children who sleep through the night and have few night waking episodes have higher cognitive attainments and easier temperaments than other children. Sleep also influences language development. To test this, researchers taught infants a faux language and observed their recollection of
7854-448: The hormone melatonin, and minimum core body temperature. Human sleep-needs vary by age and amongst individuals; sleep is considered to be adequate when there is no daytime sleepiness or dysfunction. Moreover, self-reported sleep duration is only moderately correlated with actual sleep time as measured by actigraphy , and those affected with sleep state misperception may typically report having slept only four hours despite having slept
7956-475: The hours when other people are awake, the hours when work is required, the time on clocks, etc. Time zones , standard times used to unify the timing for people in the same area, correspond only approximately to the natural rising and setting of the sun. An extreme example of the approximate nature of time zones is China, a country which used to span five time zones and now officially uses only one (UTC+8). In polyphasic sleep , an organism sleeps several times in
8058-489: The latter have been found in a GWAS study that primarily detects correlations (but not necessarily causation), other genes have been shown to have a more direct effect. For instance, mice lacking dihydropyrimidine dehydrogenase (Dpyd) had 78.4 min less sleep during the lights-off period than wild-type mice. Dpyd encodes the rate-limiting enzyme in the metabolic pathway that catabolizes uracil and thymidine to β- alanine , an inhibitory neurotransmitter . This also supports
8160-437: The major role of sleep does not appear to be rest for the body, but rest for the brain. When sleep-deprived humans sleep normally again, the recovery percentage for each stage of sleep is not the same. Only seven percent of stages one and two are regained, but 68 percent of stage-four slow-wave sleep and 53 percent of REM sleep are regained. This suggests that stage-four sleep (known today as the deepest part of stage-three sleep)
8262-452: The memory processes during sleep as well as facilitating emotional memory consolidation. Acetylcholine plays an essential role in hippocampus-dependent memory consolidation. An increased level of cholinergic activity during SWS is known to be disruptive for memory processing. Considering that acetylcholine is a neurotransmitter that modulates the direction of information flow between the hippocampus and neocortex during sleep, its suppression
8364-422: The middle of the night. Circadian rhythm exerts some influence on the nighttime secretion of growth hormone. The circadian rhythm influences the ideal timing of a restorative sleep episode. Sleepiness increases during the night. REM sleep occurs more during body temperature minimum within the circadian cycle, whereas slow-wave sleep can occur more independently of circadian time. The internal circadian clock
8466-496: The morning than are fifteen-year-olds. Chronotypes far outside the normal range are called circadian rhythm sleep disorders. Naps are short periods of sleep that one might take during the daytime, often in order to get the necessary amount of rest. Napping is often associated with childhood, but around one-third of American adults partake in it daily. The optimal nap duration is around 10–20 minutes, as researchers have proven that it takes at least 30 minutes to enter slow-wave sleep,
8568-508: The most benefits to learning. The benefits to alertness show no change based on duration of the nap for combating post-lunch dip , even for naps as short as 10 minutes. Napping enhances alertness in young adults and adolescents during afternoons’ performances, which affect efficiency. Additionally, pre-teens who nap regularly during the day demonstrate better sleep at night. In younger children, napping increased drowsiness even while improving memory recall. For students of all ages, napping during
8670-405: The night and density of eye movements. Sleep duration can also vary according to season. Up to 90% of people report longer sleep duration in winter, which may lead to more pronounced seasonal affective disorder . By the time infants reach the age of two, their brain size has reached 90 percent of an adult-sized brain; a majority of this brain growth has occurred during the period of life with
8772-613: The occurrence of deep slow-wave sleep , intended to quickly revitalize the napper. The power nap is meant to maximize the benefits of sleep versus time. It is used to supplement normal sleep, especially when a sleeper has accumulated a sleep deficit . The greater the sleep deficit, the more effective the nap. It has been shown that excessive daytime sleepiness (EDS) can be improved by prescribed napping in narcolepsy . Apart from narcolepsy, it has not been demonstrated that naps are beneficial for EDS in other sleep disorders. Research suggests that shorter, habitual naps after instruction offer
8874-466: The period of a person being awake, and they continue to transition into Stage 1 of sleep and in stage 2. Delta waves are seen in stages 3 and 4 of sleep when a person is in their deepest of sleep. Sleep is divided into two broad types: non-rapid eye movement (non-REM or NREM) sleep and rapid eye movement (REM) sleep. Non-REM and REM sleep are so different that physiologists identify them as distinct behavioral states. Non-REM sleep occurs first and after
8976-453: The phase of sleep and the type of memory. For example, declarative and procedural memory-recall tasks applied over early and late nocturnal sleep, as well as wakefulness controlled conditions, have been shown that declarative memory improves more during early sleep (dominated by SWS) while procedural memory during late sleep (dominated by REM sleep) does so. Slow-wave sleep Slow-wave sleep ( SWS ), often referred to as deep sleep ,
9078-451: The proportion of REM sleep increases in the two cycles just before natural awakening. Awakening can mean the end of sleep, or simply a moment to survey the environment and readjust body position before falling back asleep. Sleepers typically awaken soon after the end of a REM phase or sometimes in the middle of REM. Internal circadian indicators , along with a successful reduction of homeostatic sleep need, typically bring about awakening and
9180-462: The reactivation of individual memory representations was significantly higher during SWS as compared to other sleep stages. Affective representations are generally better remembered during sleep compared to neutral ones. Emotions with negative salience presented as a cue during SWS show better reactivation, and therefore an enhanced consolidation in comparison to neutral memories. The former was predicted by sleep spindles over SWS, which discriminates
9282-550: The recovery of the brain from daily activities. Prior to 2007, the term SWS referred to both the third and fourth stages of NREM. However, after both stages were combined into stage three, SWS refers only to the third stage. This period of sleep is called slow-wave sleep because the EEG activity is synchronized, and characterised by slow waves with a frequency range of 0.5–4.5 Hz and a relatively high amplitude power with peak-to-peak amplitude greater than 75 μV. The first section of
9384-435: The role of β-alanine as a neurotransmitter that promotes sleep in mice. Familial natural short sleep is a rare, genetic, typically inherited trait where an individual sleeps for fewer hours than average without suffering from daytime sleepiness or other consequences of sleep deprivation . This process is entirely natural in this kind of individual, and it is caused by certain genetic mutations. A person with this trait
9486-400: The rules for that language. Infants who slept within four hours of learning the language could remember the language rules better, while infants who stayed awake longer did not recall those rules as well. There is also a relationship between infants' vocabulary and sleeping: infants who sleep longer at night at 12 months have better vocabularies at 26 months. Children can greatly benefit from
9588-511: The school day showed benefits to reaction time and recall of declarative memory of new information, especially if the naps remain in slow-wave sleep , i.e. less than an hour in length. In adults, a causal association has been found between habitual daytime napping and larger brain volume. Brain volume normally declines with age, and is associated with neurodegenerative disease . Earlier studies have shown benefits of napping for cognitive performance for healthy adults. The circadian cycle plays
9690-471: The screens of electronic devices such as smartphones and televisions, which emit large amounts of blue light, a form of light typically associated with daytime. This disrupts the release of the hormone melatonin needed to regulate the sleep cycle . The most pronounced physiological changes in sleep occur in the brain. The brain uses significantly less energy during sleep than it does when awake, especially during non-REM sleep. In areas with reduced activity,
9792-400: The suprachiasmatic nucleus has a direct neural connection to the pineal gland , which releases the hormone melatonin at night. Cortisol levels typically rise throughout the night, peak in the awakening hours , and diminish during the day. Circadian prolactin secretion begins in the late afternoon, especially in women, and is subsequently augmented by sleep-induced secretion, to peak in
9894-561: The table below. Sleep may facilitate the synthesis of molecules that help repair and protect the brain from metabolic end products generated during waking. Anabolic hormones, such as growth hormones , are secreted preferentially during sleep. The brain concentration of glycogen increases during sleep, and is depleted through metabolism during wakefulness. The human organism physically restores itself during sleep, occurring mostly during slow-wave sleep during which body temperature, heart rate, and brain oxygen consumption decrease. In both
9996-421: The trough of the cycle. A healthy young adult entrained to the sun will (during most of the year) fall asleep a few hours after sunset, experience body temperature minimum at 6 a.m., and wake up a few hours after sunrise. Generally speaking, the longer an organism is awake, the more it feels a need to sleep ("sleep debt"). This driver of sleep is referred to as Process S . The balance between sleeping and waking
10098-527: The wave signifies a "down state", an inhibition or hyperpolarizing phase in which the neurons in the neocortex are silent. This is the period when the neocortical neurons are able to rest. The second section of the wave signifies an "up state", an excitation or depolarizing phase in which the neurons fire briefly at a high rate. The principal characteristics during slow-wave sleep that contrast with REM sleep are moderate muscle tone , slow or absent eye movement , and lack of genital activity. Prior to 2007,
10200-459: Was a lower percentage of SWS in African Americans compared to Caucasians, but since there are many influencing factors (e.g., body mass index , sleep-disordered breathing, obesity , diabetes , and hypertension ), this potential difference must be investigated further. Mental disorders play a role in individual differences in the quality and quantity of SWS: subjects with depression show
10302-565: Was no effect of napping for as long as 40 minutes per day, but a sharp increase in risk of disease occurred at longer nap times. No causal relationship was established: the link may be to do with people taking a longer nap in response to the pre-existence of other risk factors. Habitual naps are also an indicator of neurological degradation such as dementia in the elderly, as reduction in brain function causes more sleepiness. For idiopathic hypersomnia , patients typically experience sleep inertia and are unrefreshed after napping. How long and when
10404-419: Was significantly higher than the signals observed during the control tasks, which involved similar visual stimulation and cognitively-demanding tasks but did not require learning. This associated with the spontaneously occurring wave oscillations that account for the intracellular recordings from thalamic and cortical neurons. Specifically, SWS presents a role in spatial declarative memory . Reactivation of
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